Syntheses of rare earth metal complexes with aminopolycarboxylic acids and study on structural changes: Nine-coordinated mononuclear K2[Dy III (dtpa)(H2O)]·6H2O and binuclear K4[Ho III 2(dtpa)2]·4H2O
The crystal and molecular structures of mononuclear K2[Dy III (dtpa)(H2O)]·6H2O (H5dtpa?= diethylenetriaminepentaacetic acid) and binuclear K4[Ho III 2(dtpa)2]·4H2O complexes have been determined by single-crystal X-ray structure analyses. The crystal of K2[Dy III (dtpa) (H2O)]·6H2O complex belongs to the triclinic crystal system, space group. The [Dy III (dtpa)(H2O)] 2- complex anion has a nine-coordinate pseudo-monocapped square antiprismatic structure, in which the nine coordinated atoms (three N and six O) are from one dtpa ligand and one water molecule. The crystal of K4[Ho III 2(dtpa)2]·4H2O complex belongs to triclinic crystal system, space group. The [Ho III 2(dtpa)2] 4- complex anion is composed of two identical parts and every Ho III O6N3 has a nine-coordinate, distorted monocapped square antiprismatic structure, in which the dtpa ligand coordinates to one central Ho III ion with three N atoms and five O atoms and to the other Ho III ion with one O atom in the same coordinated carboxylic group. Although the Dy III and Ho III ions have close ionic radii (1.052 and 1.041?Å) and electronic configuration (f? 9 and f 10 ) they form mononuclear and binuclear nine-coordinate complexes, respectively. Perhaps there is a critical ionic radius for mononuclear and binuclear structures, namely the dtpa complexes of rare earth metals with larger ionic radii than 1.052?Å of Dy III ion adopt a mononuclear nine-coordinate structure, while those with smaller ionic radii than 1.041?Å of Ho III ion adopt a binuclear nine-coordinate structure.
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